As the dimension of a semiconductor device is getting less, the gate structure and the thickness of the gate insulation layer are reduced accordingly. However, a leakage current occurs when the gate insulation layer of silicon oxide becomes thinner. To address the current leakage, high-k/metal gate (HK/MG) technology is used in semiconductor structure, adopting high-k material to replace silicon oxide, and metal gate to replace polysilicon gate accordingly. The HK/MG technology can facilitate the gate close/open rate and reduce current leaked from gate to body.
For the HK/MG technology, there are layers of films deposited on the metal gate, and good particle source control (i.e., solid source precursor of particle free) is required to avoid pits defect within metal gate during the deposition of the films. Any kind of particle source come from solid source precursor would easily impact performance of the semiconductor device.
To deposit films on the metal gate, atomic layer deposition (ALD) is used extensively. ALD is a process using precursor materials as a source to deposit the required film on a substrate, the precursor can be gas, liquid, or solid, and the precursor is transformed into its gas state for deposition. For instance, if a solid precursor is used, untransformed small particles from the solid precursor may fall on a semiconductor wafer center during carrier gas delivery and block the subsequent gate filling process within poly removal metal gate. Small particle is a strong blocking particle that would block the gate filling process and cause pits defect after chemical mechanical polishing (CMP), which affects the performance of the semiconductor device.
The above situation can be reduced by thermal caking, which uses heat to fuse particles of the solid precursor to become a cake of precursor in a container. However, the cake is still apt to crack and induce ultra-small particles during transportation of the container. In order to remove the ultra-small particles, it takes extra time to dump cracked solid precursor up to about one fifth of the solid precursor. Therefore, there is a need for a method to avoid the forming of small particles or ultra-small particles, and to facilitate the semiconductor fabrication.